There is evidence of a giant planet lurking in the outer solar system at more than a thousand
times the distance from the Sun as Earth, and could be as much as 25,000 times fainter
than Pluto.
Astronomers are gazing into the abyss in search of Planet Nine. Welcome back to Launch Pad,
I'm Christian Ready, your friendly neighborhood astronomer. In our previous video, we looked
at evidence for a large planet that would be lurking in the outer solar system.
And this planet would explain the orbital clustering of several trans-Neptunian objects.
However, evidence of a planet is not nearly as good as finding the planet itself.
In this video, we're going to talk about how astronomers are doing just that.
Mike Brown and Konstantin Batygin of Caltech ran several computer simulations to determine
what kinds of orbits Planet Nine could have.
But all of them are highly elongated and tend to point away from the clustered objects.That
means from our vantage point here on Earth, Planet Nine’s possible orbits are confined to a
band encircling us around the sky.
Even so, this band is a really large search area.
Fortunately, there are some clues that help us narrow down where in the sky to search.
Planet Nine is estimated to be about 10 times more massive than Earth, and comes no closer
than about 300 astronomical units to the Sun.
Even though that's 10 times farther from the Sun than Neptune, Planet Nine should still
have been bright enough to have been detected in previous surveys.
An examination of recent surveys showed no evidence for such a planet.
This suggests that Planet Nine is probably near its farthest point from the Sun, or aphelion.
And that makes sense because as planets approach perihelion, they speed up, whereas when they
approach aphelion, they slow down.
Planet Nine should therefore spend most of its 20,000 year orbit near aphelion.
But its aphelion distance could be as much as 1,000 astronomical units.
At that distance, Planet Nine would be 25,000 times fainter than Pluto.
Telescopes like Keck and Hubble should have no trouble spotting Planet Nine, but their
fields of view are incredibly small, and the search area in Taurus and Orion is something
like 4,000 times the size of the full Moon.
So using Keck or Hubble would be like squinting through a soda straw. But
there is a telescope that's right next door to Keck.
It's the 8.2 meter, Subaru telescope, the national telescope of Japan.
Subaru is equipped with the Hyper Suprime-Cam, an 870 megapixel camera that can capture 6
full moons’ worth of sky in a single image.
Planet Nine's aphelion should be somewhere between the constellations Orion and Taurus,
making the search area visible from September through February of every year.
Subaru should be able to cover the search area in about 20 nights.
That may not seem like a lot of time, but astronomers using Subaru to search for Planet
Nine have to compete with other astronomers for time on the telescope.
Not only that but, bad weather interfered with the first two years of Planet Nine searching,
so only a fraction of the search area has been covered to date.
At this rate, it'll probably take a few more years before the entire Planet Nine search
area is completely covered.
Luckily, a second team of astronomers led by Scott Sheppard from Carnegie Science are
also using Subaru to conduct their own search for Planet Nine.
Even better, Sheppard’s team are also piggybacking on another survey with another telescope.
The Dark Energy Survey uses the 4-meter Victor Blanco Telescope at the Cerro Tololo Inter-American
Observatory in Chile.
The telescope used the Dark Energy Camera, or DECam mounted at the telescope's prime
focus.
DECam’s field of view is twice the Hyper Suprime-Cam mounted on the Subaru telescope.
But its detector is 300 megapixels smaller and it's mounted to a telescope that is half
the size of Subaru.
Even so, Sheppard and his team used the Blanco telescope to discover several new trans-Neptunian
objects that are even fainter than Planet Nine is predicted to be.
So this tells us that the search for Planet Nine is in fact possible.
And by the way, these objects all follow orbits that are clustered in a manner that is consistent
with Planet Nine.
Now you may be wondering how is it they keep finding these tiny objects when there's supposedly
a giant planet they haven't found yet?
Well the answer is we expect there to be thousands, maybe even hundreds of thousands of these
tiny objects, but only one giant planet.
It's like going fishing in the ocean - you expect to catch a lot of small fish, but you
don't expect to catch a whale.
But what if neither the Subaru nor Blanco telescopes find Planet Nine?
That would be unfortunate, but it would’t necessarily rule out the planet's existence.
It could mean it's simply on a different part of its orbit, so a different region of the
sky would need to be searched.
Or it could be that Planet Nine is on a much larger orbit than predicted, and its aphelion
would carry it farther away, making it too faint to be detected by Subaru.
But there is another possibility which kinda gives us the screaming heebie-jeebies.
Planet Nine could be passing in front of the Milky Way, lost in the glare of a crowded
field of bright background stars.
Fortunately, there’s a telescope under construction that should be able to resolve Planet Nine
even among such a crowded field.
The Large Synoptic Survey Telescope will make the widest and deepest scan of the southern
sky over the course of a decade.
LSST will be armed with an 8.4 meter mirror, and a gigantic, 3 Gigapixel camera with a
9.6 square degree field of view.
That will give LSST the sensitivity and clarity to distinguish Planet Nine even if it’s
fainter than expected, and even if it’s passing across the Milky Way.
Not only that, but LSST will complete a full scan of the entire sky once every five to
seven days and repeat over and over again for a decade.
That means that every point in the sky will be imaged by LSST more than 800 times.
This means that if Planet Nine is on a completely different orbit, or if it's farther and fainter
than expected, LSST should be able to detect it as long as it's somewhere in the southern
sky.
Meanwhile, the search for Planet Nine continues.
It's November 2018, and Mike Brown and his team have time scheduled on Subaru in December.
This will mark the third year searching for Planet Nine, and hopefully a little bit more
of the sky will be covered.
But each year brings new discoveries of distant objects in the outer solar system, each of
which seem to be pointing the way to Planet Nine.
There are so many new worlds waiting to be discovered, both right here in our solar system
and far beyond.
If you'd like to join me on the search for these amazing new worlds, please make sure
to subscribe and ring that notification bell so you don't miss out on any new videos.
Until next time, keep watching the skies.